Most existing mobile communication systems incorporate a cellular architecture in which geographical areas are divided into cells. Each cell contains a base station for interfacing mobile units in the cell to a mobile switching center (MSC) and a backbone wired network. The MSC connects the base stations together for communication therebetween and to provide communication with the public switched network. A base station is equipped with radio transceivers that enable rf communications over available frequency channels with mobile units in the cell.
In the area where two neighboring cells intersect, the cells overlap to form a handover region. Handover typically occurs when the signal strength or quality of a connection between a mobile unit and a base station falls below a predetermined threshold. This generally occurs when the mobile unit enters the handover region at the edge of a cell. As the mobile unit moves from one cell to another, an ongoing call involving the mobile unit is handed off from a channel in the current cell to an available channel in the next cell. However, if no channel is available in the next cell, the call drops (i.e., terminates) because the mobile unit moves out of range of the base station of the current cell. Since handover requests for channels come without warning, often wireless resources are not available when needed and calls get dropped.
Dropping calls significantly effects the service quality for cellular customers. In mobile communications systems, it is important that mobile units with an established radio connection on a radio channel are able to maintain that connection when moving from one cell to another cell. Accordingly, there is a need in the art to minimize the number of calls dropped due to handover failure.